Intersexuality is a term used to describe a person whose sex chromosomes, genitalia and/or secondary sex characteristics are determined to be neither exclusively male nor female. A person with intersex may have biological characteristics of both the male and female sexes. Family medical practitioner, research psychologist and popular author Leonard Sax describes intersexuality as

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conditions in which chromosomal sex is inconsistent with phenotypic sex, or in which the phenotype is not classifiable as either male or female. Applying this ... precise definition, the true prevalence of intersex is seen to be about 0.018%.[1]

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Research in the late twentieth century has led to growing medical consensus that the diverse intersex physicalities are normal, but relatively rare, forms of human biology. Perhaps the most prominent researcher, Milton Diamond, stresses the importance of care in selection of language related to intersexuality.

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Foremost, we advocate use of the terms "typical," "usual," or "most frequent" where it is more common to use the term "normal." When possible avoid expressions like maldeveloped or undeveloped, errors of development, defective genitals, abnormal, or mistakes of nature. Emphasize that all of these conditions are biologically understandable while they are statistically uncommon.[2]

Intersex individuals are treated in different ways by different cultures. In some cultures intersex people were included in larger "third gender" or gender-blending social roles along with other individuals. In most societies, intersexed individuals have been expected to conform to either a male or female gender role.

Whether or not they were socially tolerated or accepted by any particular culture, the existence of intersex people was known to many ancient and pre-modern cultures. Theological, moral, social and literary treatment of accommodating for them is as old as history.

As an example, one of the Sumerian creation legends Enki and Ninmaḫ (more than 4,000 years old) has Ninmaḫ, a mother-goddess, fashioning mankind out of clay. She boasts that she will determine the fate – good or bad – for all she fashions. Enki, the father god, retorts as follows.

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56-61. Enki answered Ninmaḫ: "I will counterbalance whatever fate -- good or bad -- you happen to decide." Ninmaḫ took clay from the top of the abzu [heaven] in her hand and she fashioned from it first a man who could not bend his outstretched weak hands. Enki looked at the man who cannot bend his outstretched weak hands, and decreed his fate: he appointed him as a servant of the king.

... [Three men and one woman with atypical biology are formed and Enki gives each of them various forms of status to ensure respect for their uniqueness] ...

75-78. Sixth, she fashioned one with neither penis nor vagina on its body. Enki looked at the one with neither penis nor vagina on its body and gave it the name Nibru [eunuch(?)], and decreed as its fate to stand before the king.

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Since the rise of modern medical science in Western societies, some intersex people with ambiguous external genitalia have had their genitalia surgically modified to resemble either male or female genitals. Ironically since the advancements in surgery have made it possible for intersex conditions to be concealed, many people are not aware of how frequently intersex conditions arise in human beings or that they occur at all. Contemporary social activists, scientists and health practioners, among others, have begun to revisit the issue and awareness of the existence of physical sexual variation in human beings is returning.

There are increasing calls for recognition of the various degrees of intersex as healthy variations which should not be subject to correction. Some have attacked the common Western practice of performing corrective surgery on the genitals of intersex people as a Western cultural equivalent of female genital cutting. Despite the attacks on the practice, most of the medical profession still supports it, although activism has radically altered medical policies and how intersex patients and their families are treated. Others, typically social conservatives, have claimed that the talk about third sexes represents an ideological agenda to deride gender as a social construct whereas they believe binary gender (i.e. there is only male and female) is a biological reality.

Depending on the type of intersex condition, corrective surgery may not be necessary for protection of life or health, but purely for aesthetic or social purposes. Unlike other aesthetic surgical procedures performed on infants, such as corrective surgery for a cleft palate, genital surgery may lead to negative consequences for sexual functioning in later life (such as loss of sensation in the genitals, for example, when a clitoris deemed too large/penile is reduced/removed, or feelings of freakishness and unacceptability) which would have been avoided without the surgery; in other cases negative consequences may be avoided with surgery. Opponents maintain that there is no compelling evidence that the presumed social benefits of such "normalizing" surgery outweigh the potential costs.[3](Similar attitudes are present in some cases of botched infant circumcision, in which the solution might involve intensive medical and parental efforts to reassign the male baby to a female identity, which oppenents claim lead to the degrading interpretation that females are essentially castrated males. This view overlooks the embryological origin of the penis/clitoris.) Defenders of the practice argue that it is necessary for individuals to be clearly identified as male or female in order for them to function socially. However, many intersex individuals have resented the medical intervention, and some have been so discontented with their surgically assigned gender as to opt for sexual reassignment surgery later in life.

During the Victorian Period, medical authors introduced the terms "true hermaphrodite" for an individual who has both ovarian and testicular gonadal histology, verified under a microscope, "male pseudo-hermaphrodite" for a person with testicular tissue, but either female or ambiguous sexual anatomy, and "female pseudo-hermaphrodite" for a person with ovarian tissue, but either male or ambiguous sexual anatomy. The writer Anne Fausto-Sterlingcoined the words herm (for "true hermaphrodite"), merm (for "male pseudo-hermaphrodite"), and ferm (for "female pseudo-hermaphrodite"), and proposed that these be recognized as sexes along with male and female. However, her use was "tongue-in-cheek"; she no longer advocates these terms even as a rhetorical device, and her proposed nomenclature was criticized by Cheryl Chase, in a letter to The Sciences which criticized the traditional standard of medical care as well as Fausto-Sterling's shorter names, and announced the creation of the Intersex Society of North America.

The terms hermaphrodite and pseudohermaphrodite, introduced in the 19th century, are now considered problematic.[4] The phrase '"ambiguous genitalia'" refers specifically to genital appearance, but not all intersex conditions result in atypical genital appearance.[5]

The Intersex Society of North America and intersex activists have moved to eliminate the term "intersex" in medical usage, replacing it with "disorders of sex development" (DSD) in order to avoid conflating anatomy with identity.[6] Members of The Lawson Wilkins Pediatric Endocrine Society[7] and the European Society for Paediatric Endocrinology[8] accepted the term "disorders of sex development" (DSD) in their "Consensus statement on management of intersex disorders" published in the Archives of Disease in Children[9] and in Pediatrics.[10] The term is defined by congenital conditions in which development of chromosomal, gonadal, or anatomical sex is atypical. However, this has been met with criticism from other activists who question a disease/disability model and advocate no legal definition of sexes, no gender assignments, no legal sex on birth certificates, and no official sexual orientation categories.[11]

Alternatives to labeling these as "disorders" have also been suggested, including Variations of Sex Development by sexologist Milton Diamond.[12]

Sax's strict definition of intersex (above) is most relevant to family practice and psychological research. Other interest groups serve different communities and concerns and so broaden the definition of intersex in these fields.

The Intersex Society of North America (ISNA) comments that perhaps 1 percent of live births exhibit some degree of sexual ambiguity,[13] and that between 0.1% and 0.2% of live births are ambiguous enough to become the subject of specialist medical attention, including surgery to disguise their sexual ambiguity. In fact, the ISNA figure is derived from Anne Fausto-Sterling, an academic in gender studies, who includes AIS, CAH, ambiguous genitalia, and mosaic chromosomes (mosaicism), in addition to sex chromosome aneuplodies, and any deviations from "the Platonic ideal." This means she includes:

hypospadias, the placement of the urinary meatus on underside of the penis or at the base, instead of at the end; and,

The prevalence of intersex is important to Fausto-Sterling's theory of gender. In Sexing the Body: Gender Politics and the Construction of Gender, she claims that 1.7 percent of human births are intersex.[14] She writes,

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While male and female stand on the extreme ends of a biological continuum, there are many bodies [...] that evidently mix together anatomical components conventionally attributed to both males and females. The implications of my argument for a sexual continuum are profound. If nature really offers us more than two sexes, then it follows that our current notions of masculinity and femininity are cultural conceits.

[...] Modern surgical techniques help maintain the two-sex system. Today children who are born "either/or-neither/both" — a fairly common phenomenon — usually disappear from view because doctors "correct" them right away with surgery.[14]

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However, inspection of the descriptions of specific intersex variations (below) will show that these do not form any "continuum", nor do they change the objective differences between typical male and female forms. The intersex variations each describe a unique type of human physicality.

During fertilization, the sperm adds either an X (female) or Y (male) chromosome to the X in the ovum. This determines the genetic sex of the embryo.[15] During the first weeks of development, genetic male and female fetuses are "anatomically indistinguishable," with primitive gonads beginning to develop during approximately the sixth week of gestation. The gonads, in a "bipotential state," may develop into either testes, the male gonads, or ovaries, the female gonads, depending on the consequent events.[15] By the seventh week, male and female fetuses are identical.

At around eight weeks of gestation, the gonads of an XY embryo differentiate into functional testes, secreting testosterone. Ovarian differentiation, for XX embryos, does not occur until approximately Week 12 of gestation. In normal female differentiation the müllerian duct system develops into the uterus, Fallopian tubes, and inner third of the vagina.
In males the müllerian duct-inhibiting hormone MIH causes this duct system to regress. Next, androgens cause the development of the Wolffian duct system, which develops into the vas deferens, seminal vesicles, and ejaculatory ducts.[15]
By birth, the typical fetus has been completely "sexed" male or female, the hormones and genital development remaining consistent with the genetic sex.

In androgen insensitivity syndrome, a genetic male with XY chromosomes is otherwise female. The body fails to respond to the testosterone produced by the testes, due to an androgen receptor defect.[16]
During development, the testes form, but due to the body's insensitivity to the testosterone responsible for the differentiation into Wolffian structures (epididymis, vas deferens, and seminal vesicles) the body differentiates along the female path. Kolodny et al. write,

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Certain hormonal conditions must exist for male development to ensue, even if the sex chromosome pattern is 46,XY.[15]

The common habit in the 21st century of elevating the role of the sex chromosomes above all other factors when determining gender may be analogous to the older habit of finding "true" sex in the gonads. Though high school biology teaches that men have XY and women XX chromosomes, in fact there are quite a few other possible combinations such as Turner syndrome XO, Triple X syndrome XXX, Klinefelter syndrome XXY, XYY syndrome XYY, Mosaicism XO/XY, de la Chapelle syndrome XX male, Swyer syndrome XY female, and there are many other individuals who do not follow the typical patterns (such as individuals with four or even more sex chromosomes).

Thus, people nowadays may be more likely to look towards the sex chromosomes than, for example, the histology of the gonads. However, according to researcher Eric Vilain at the University of California, Los Angeles, "the biology of gender is far more complicated than XX or XY chromosomes".[17] Many different criteria have been proposed, and there is little consensus.[18]

People with AIS have typically male chromosomes (XY), along with typically female appearance and genitalia.

Although people with AIS have a vagina, they lack a uterus, cervix of the uterus, and ovaries, and are thereby infertile. The vagina may be shorter than average; in some cases it is nearly absent. Instead of female internal reproductive organs, a person with AIS has undescended or partially descended testes, of which she may not even be aware.

At puberty, a child with AIS develops breasts and a feminine shape.[14] In normal women, both testosterone and estrogen are present, but since the bodies of AIS women do not recognize testosterone, it is converted to estrogen. Testosterone is responsible for the growth of pubic and axillary hair, so many women with AIS have no hair in these areas, or have only sparse hair. Primary amenorrhea (absence of menstruation) is another sign of AIS.[19]

Except in the case of spontaneous mutation, AIS is an inherited condition. It is possible to diagnose AIS during the ninth to 12th week of pregnancy, using chorionic villus sampling, and it can be detected by ultrasound and amniocentesis by Week 16, although prenatal diagnosis of AIS is not indicated unless a family history of AIS is known.[20]

An AIS female may be unaware of her condition. Symptoms of primary amenorrhea, lack of pubic and axillary hair, and what appears to be a hernia can lead a female with AIS to present these indicators to a doctors, leading to the discovery of AIS. Individuals with complete AIS typically identify as female.[19] Nevertheless, surgery and other techniques may be used to make the genital appearance more "typically female."

To lengthen the vagina, a woman with AIS may be instructed by a doctor to apply regular pressure dilation several times a day.[21]Vaginoplasty, the surgical shaping of the vagina, and clitoridectomy, removal of the clitoris, may also be performed.

In CAIS, the body reads no "male" hormones. In partial androgen insensitivity syndrome (PAIS), however, the body reads some androgens, so virilization occurs to a certain degree. PAIS results in genitalia that may be ambiguous, due to some, although limited, metabolization of the hormones produced by the testes. Ambiguous genitalia most frequently appear as a large clitoris, known as clitoromegaly, or a small penis, which is called as micropenis or microphallus.

The equivalent of genetic males’ AIS is congenital adrenal hyperplasia affecting genetic females. CAH is a genetic disorder in which the adrenal glands "while trying to make cortisone, may make an unusually high level" of masculinizing hormones. When CAH occurs in an XY embryo, this is not an intersex condition, but amongst XX individuals it is one of the most frequent forms of intersexuality.[20]

Due to a defect in the enzyme that synthesizes adrenal hormones, a blockage in one synthetic pathway will occur, causing excessive production of androgenic hormones in a different pathway, virilizing an XX fetus in utero. Genitalia may appear completely masculine, or it may be ambiguous.[22]

In genetic females, common signs of CAH include clitoromegaly, labia that resemble a scrotum, and masculine-typical characteristics, including a deep voice and dense body hair.[20]

In either the case of AIS or CAH, testing of the chromosomes can be done to determine the genetic sex of the individual.

Typical males have sex chromosomes XY and typical females XX. One biological definition of a male child is the presence of a Y chromosome. This definition has sometimes been used for sex determination at sports events, but it caused much confusion because it does not always apply.[23]

The most common cause of sexual ambiguity is congenital adrenal hyperplasia, an endocrine disorder in which the adrenal glands produce abnormally high levels of virilizing hormones. In genetic females, this leads to an appearance that may be slightly masculinized (large clitoris) to quite masculine.

A single X chromosome (XO) is called Turner's syndrome. It is characterized by a lack or incomplete development of certain primary and secondary female characteristics and is associated with a range of medical issues.

Sex chromosomal mosaicism or chimerism can cause what was once called "true hermaphroditism", the presence of both testicular and ovarian tissue in one individual.

Androgen insensitivity syndrome. They develop either partially or fully as females, due to their bodies failing to respond to testosterone. In the case of complete androgen insensitivity syndrome (CAIS), their tissues are totally insensitive to androgens, and they will develop as females, with normal female external organs. However, they will not develop a uterus or fallopian tubes, due to the production of Müllerian inhibiting factor by their testes. At puberty breasts will develop due to the production of estrogen by the testes; but no menstruation will occur due to the lack of a uterus. The tissues of individuals with partial androgen insensitivity, by contrast, have partial sensitivity to testosterone, but it is reduced compared to the male normal. These individuals can develop with either male external anatomy, or female external anatomy, or some combination, depending on the degree of insensitivity.

5-alpha-reductase deficiency. In this condition, individuals have testes, as well as vagina and labia, but with a small penis capable of ejaculation instead of a clitoris (this penis, however, appears to be a clitoris at birth). These individuals are normally raised as girls. However, come puberty, their testes will descend, their voice will deepen and they often will develop a male sexual identity. People with this deficiency develop only limited facial hair. The number of people with this condition varies geographically, depending on how much of a given population is interrelated.

Excessive in utero exposure to androgens may lead to intersex in XX cases:

Progestin-induced virilisation. In this case, the male hormones are caused by use of progestin, a drug that was used in the 1950s and 1960s in order to prevent miscarriage. These individuals have internal and external female anatomy. They develop however some male secondary characteristics and they frequently have unusually large clitorises.

A similar phenomenon occurs in cases where a cow brings two fraternal twins, one male and one female, to term. Because (unlike humans) such twins share hormones via their placental blood interface with the mother cow, male hormones produced in the body of the fetal bull find their way into the body of the fetal cow and masculinize her brain. The result is a freemartin (unconventional heifer), a cow that will eventually try to mount other cows the way that a bull would.

In XX male syndrome (also called de la Chapelle syndrome) the resulting child is usually a phenotypically normal male, but without sperm production. This syndrome is sometimes the result of an abnormal interchange of the SRY region from a Y chromosome to an X.

With some conditions of intersex, even the chromosomal sex may not be clear. A "true hermaphrodite" is defined as someone with both male gonadal tissue (testes) and female gonadal tissue (ovarian tissue).

In 2004, researchers at UCLA published their studies of a lateral gynandromorphic hermaphroditic bird, which had a testicle on the right and an ovary on the left. Its entire body was split down the middle between male and female, with hormones from both gonads running through the blood.[24]

This extreme example of hermaphroditism is not the case for humans, among whom there is a spectrum of forms of ovotestes. The varieties range, including having two ovotestes or having one ovary and one ovotestis. This is often in the form of streak gonads. Phenotype is not determinable from the ovotestes; in some case the appearance is "fairly typically female," in others it is "fairly typically male," and it may also be "fairly in-between in terms of genital development."[20]

Testicular tissue holds the risk of developing into cancer, so doctors either remove it or monitor it carefully. The same is true of AIS.

A person with a mosaic karyotype has differing types of karyotypes amongst different cells, due to incorrect division early in the life of the embryo. For example, it is possible to have both XX and XY cells.[20]

In typical fetal development, the presence of the SRY gene causes the fetal gonads to become testes; the absence of it allows the gonads to continue to develop into ovaries. Thereafter, the development of the internal reproductive organs and the external genitalia is determined by hormones produced by certain fetal gonads (ovaries or testes) and the cells' response to them. The initial appearance of the fetal genitalia (a few weeks after conception) is basically feminine: a pair of "urogenital folds" with a small protuberance in the middle, and the urethra behind the protuberance. If the fetus has testes, and if the testes produce testosterone, and if the cells of the genitals respond to the testosterone, the outer urogenital folds swell and fuse in the midline to produce the scrotum; the protuberance grows larger and straighter to form the penis; the inner urogenital swellings grow, wrap around the penis, and fuse in the midline to form the penile urethra.

Because there is variation in all of these processes, a child can be born with a sexual anatomy that is typically female, or feminine in appearance with a larger than average clitoris (clitoral hypertrophy); or typically male, masculine in appearance with a smaller than average penis that is open along the underside. The appearance may be quite ambiguous, describable as female genitals with a very large clitoris and partially fused labia, or as male genitals with a very small penis, completely open along the midline ("hypospadic"), and empty scrotum.

There are dozens of named medical conditions that may lead to intersex anatomy. Fertility is variable. The distinctions "male pseudohermaphrodite", "female pseudohermaphrodite" and especially "true hermaphrodite" are vestiges of 19th century thinking that placed "true sex" in the histology (microscopic appearance) of the gonads.

According to the New England Journal of Medicine, vol 338, p 166, physicians in the Western General Hospital, Edinburgh, Scotland have reported on a child with a penis, one testicle, and an ovary and fallopian tube instead of a second testicle. Some of this child's body cells are XY (male), and some are XX (female). The child was conceived as the result of in-vitro fertilization, and it appears most likely that two embryos, a male embryo and a female embryo, fused before or soon after embryos were transferred to the mother's uterus.

This kind of condition, where there is more than one set of cell lines with different sets of chromosomes making up the body, is known as chimerism. This kind of tetraploid chimerism can also occur naturally, without in-vitro fertilization.[26]

However, not all cases of Chimerism involve intersex. There have been about 40 known cases worldwide of humans reproducing naturally and producing offspring with absolutely no genetic similarities between mother and child. Discovery Health Channel has produced a documentary, "I Am My Own Twin," on two families dealing with chimerism.

↑Groveman, Sherri A. (1999), "The Hanukkah Bush: Ethical Implications in the Clinical Management of Intersex.", in Dreger, Alice Domurat, Intersex in the Age of Ethics, Hagerton: University Publishing Press, pp. 23-28